[Containment] Set validity in locator

Set validity of selected location from locator control, to
disallow creation when no valid location is selected (which
is possible due to containment rules.) WTD-962.

platform/commonUI/browse/src/creation/LocatorController.js

@@ -34,8 +34,17 @@ define(
                             $scope.structure.validate(priorObject) ?
                                     priorObject : undefined
                         );
+                        return;
                     }
                 }
+
+                // Set validity
+                if ($scope.ngModelController) {
+                    $scope.ngModelController.$setValidity(
+                        'composition',
+                        !!$scope.treeModel.selectedObject
+                    );
+                }
             }
 
             // Initial state for the tree's model